Professor McGonagall never once sat her own detentions. Only 3 different teachers gave Harry and his friends detention through the course of the series, but the other 2 (Snape and Umbridge) both stood over them as they did whatever punishment was assigned. McGonagall, however, pawned them off on Hagrid, Lockhart, and Filch for their detentions. I guess McGonagall didn't feel the need to lecture Harry, Ron, or Hermione while they did their detentions, as Snape and Umbridge seemed to feel to need to do. Has anyone else noticed this?
He thrusts his fists against the posts and still insists he sees the ghosts
Or McGonagall just didn't like being on detention duty or was too busy to do so. I think Snape just got a perverse pleasure watching Harry in detention and Umbridge used detention to try to get Harry to break to her will.
It is recurring to me that she did Harry and Ron detention once in Harry Potter and the Chamber of Secrets when they had missed the train, and instead they opted to use the Weasley's flying car to Hogwarts, and ran into the tree. Snape had wanted to expel them, and would have if they had been in Slytherin. And she said she would be writing to their families, I doubt the Dursleys would have cared in the least. Plus she might have been a senior teacher in bewitch she got special priviagles that other teachers didn't have. And plus you have to remember that she was nicer then some of the other teachers. Like how you mention Snape and Umbridge did. Remember that Harry Potter was telling the truth, but Umbridge didn't want to listen, and thought he was lying and didn't like him talking about of turn. But she wasn't there so how does she know if Harry Potter was lying or telling the truth? And it is possible that she didn't like doing them, or felt she did enough them in her time at teaching at Hogwarts. But both Hagrid and Lockhart liked Harry Potter, so it would be no problem to serve dentition with them, then say if she had pawned Harry Potter off to Snape even if Harry wasn't in trouble with him. I believe that he don't hate Ron as much as Harry and Hermione, even since a lot of times that Hermione would know the answers to any questions that Snape had thrown out, even to Harry as she would have read about them ahead of time.
McGonagall gave them detention for flying the car to school, but she didn't do the detentions with them. Harry was sent to Lockhart to help with fan mail, and Ron was sent to clean the trophy room with Filch.
He thrusts his fists against the posts and still insists he sees the ghosts
And from what I saw on Wikipedia that McGonagall mentions to Umbridge that she has been teaching at Hogwarts for 39 years, so that would give her even the right to serve or not serve detentions that she assigns
Yep and like you said with that power she could do anything she didn't want to do and that would including being the staff in charge of any detentions that she gave out, and I may need to watch the movie again, but other then the one detention that I mentioned in Harry Potter and the Chamber of Secrets, I don't remember her giving out any other detentions to any of the students.